Interpreting Array CGH Results

The results of array CGH testing are not always easy to understand. Sometimes, this test uncovers a change known to cause development problems, such as developmental delay or mental retardation. Other times, it shows uncertain results which require further testing of multiple family members to understand.

Although array CGH is very sensitive and cutting-edge technology, it is not flawless. It can miss certain types of chromosomal changes, which is why it is often done with chromosome analysis. Many genetic syndromes require very specific DNA testing to diagnose. Array CGH doesn't find every possible genetic mutation in every gene. Therefore, a normal result does not rule out an underlying chromosomal or genetic condition. It simply means that there aren’t deletions or duplications of DNA that can be found. Today's technology may not be advanced enough to provide an answer in some cases.

Possible Results

There are three types of possible results from an array CGH test: positive, uncertain, and negative.

Positive Result

With a positive result, the test revealed a chromosome change either known or expected to cause developmental problems. This result explains the reason for a person’s health and/or developmental concerns. When other people with the same or similar result have been studied, the result provides specific medical information for the patient, family, and doctor. It may also help figure out if there are possible risks for future pregnancies.

Depending on the type of change found, your doctor may recommend that other family members have testing. Such follow-up testing is not common when the results are clear, but in some situations, can help determine if the chromosomal change found was passed from a parent (inherited) or new in that person. It can also help doctors clarify the meaning and significance of the results.

Although a positive test result may provide a diagnosis, many genetic syndromes have a wide range of effects on a person’s appearance, medical problems, and mental functioning. No testing, including array CGH, can predict how mildly or severely a person may be affected by a specific genetic condition.

Uncertain Result

With an uncertain result, the test revealed a chromosomal change that doctors and scientists don't know exactly how to interpret. These types of changes either have never been seen before in a patient, are very small, or are thought unlikely to cause any developmental problems.

These changes are referred to as "variants of unknown significance." In such cases, additional samples from parents or other family members may be needed to get a more complete answer. If family members have the same chromosome change but don’t have any health or developmental problems, then the chromosome change is probably a normal variation and not disease-causing. However, if the chromosome change is not shared with normal, healthy family members, it may be more likely to be the cause of the patient’s problems.

Sometimes, even after family studies, it is still not clear whether the test result is the cause of the patient’s medical problems. Doctors may be able to do research to find out whether the change has been reported in other people and how they were affected by it. However, there are times when a clear answer can’t be reached, even with extra testing and research.

Negative Result

With a negative or “normal” result, the test did not show any chromosomal changes that could be found on array CGH. This could be because there really is no chromosomal change present or because there is a DNA or chromosomal change not detectable by the test. A genetic cause for the developmental problems can’t be ruled out. There may be other changes in genes or chromosomes that can’t be found with this testing. There are hundreds of known genetic syndromes that are not checked for with this test.

It may be useful for patients who have a negative array CGH result to see a specialist in genetics for a full exam and further testing, if indicated.